Touch screen finger tracking algorithm

Abstract

A method is disclosed for tracking the paths of multiple objects across the surface of a capacitive touch screen using capacitive sensing of rows and columns therefore. The method includes first storing historical information for the coordinate location of a first object. Then, the potential coordinate location for both the first object and a second object at a current and given time are determined with a first determining step. A decision is then made with a second determining step as to which of the potential coordinate locations is associated with the first object at the given time based on the stored historical information.

1 . A method for tracking the paths of multiple objects across the surface of a capacitive touch screen using capacitive sensing of rows and columns therefore, comprising the steps of:
 storing historical information for the coordinate location of a first object;   determining with a first determining step the potential coordinate location for both the first object and a second object at a current and given time; and   determining with a second determining step which of the potential coordinate locations is associated with the first object at the given time based on the stored historical information.   
     
     
         2 . The method of  claim 1 , wherein the multiple objects are fingers. 
     
     
         3 . The method of  claim 1 , wherein the historical information comprises at least a last known coordinate location at a prior time to the current and given time and wherein the second determining step comprises the steps of:
 accessing the historical information which comprises the last known coordinate location of the first object;   determining the distance between the last known coordinate location of the first object and each of the determined potential coordinate locations of the first object;   selecting the one of the determined potential coordinate locations having the minimum distance to the last known coordinate location as the current coordinate location for the first object at the current and given time; and   storing the one of the determined potential coordinate locations determined as the current coordinate location for the first object as the last known coordinate location for a future determining step.   
     
     
         4 . The method of  claim 1 , wherein the second step of determining comprises the steps of:
 predicting with the historical information a predicted location of the first object at the current and given time;   determining the distance between the predicted location and each of the determined potential coordinate locations;   selecting the one of the determined potential coordinate locations having a minimum distance to the predicted coordinate location as the current coordinate location for the first object; and   storing the one of the determined potential coordinate locations determined as the current coordinate location as the historical information for the first object for a future step of determining.   
     
     
         5 . The method of  claim 4 , wherein the historical information contains at least the last known location for the first object and a previous coordinate location prior to the last known location. 
     
     
         6 . The method of  claim 5 , wherein the step of predicting comprises:
 determining direction from the last known location to a potential new coordinate location at the given and current time; and   determining a distance based on the last known location and the previous coordinate location to define the distance of the predicted coordinate location from the last known coordinate location.   
     
     
         7 . The method of  claim 1 , wherein the historical information includes at least a last known coordinate location of the first object and a previous location of the last known coordinate location prior in time to the last known coordinate location and wherein the second determining step comprises determining which of the potential coordinate locations is associated with the first object based on one of the last known coordinate location or upon the last known coordinate location and the oldest last known coordinate location. 
     
     
         8 . The method of  claim 7 , wherein the second step of determining is based upon the last known location only or upon the combination of the last known location and the oldest known location based upon the first step of determining that the at least one axis of the determined potential coordinate locations is substantially similar. 
     
     
         9 . A method for tracking paths of multiple finger touches across a surface of a capacitive touch screen using capacitive sensing of rows and columns therefore, comprising the steps of:
 storing historical information for the x-y coordinate location of a first finger touch at a prior point in time relative to the current time;   determining with a first determining step x-y coordinates representing the x-coordinates intersecting with the first finger touch and a second finger touch and the y-coordinates intersecting with the first finger touch and the second finger touch;   determining with a second determining step which of the determined x-coordinates and which of the determined y-coordinates are associated with the first finger touch representing the current x-y coordinate position of the first finger touch on the touch screen at the current time such that the x-y coordinate position of the second finger touch can be determined to be x-y coordinate position comprised of at least the one of the determined x-coordinate or determined y-coordinate that does not comprise the x- and y-coordinate of the x-y coordinate position of the determined current position of the first finger touch; and   storing in place of the historical information at least in a portion thereof the determined x-y coordinate position of the first finger touch at the current time for use in a future determining step.   
     
     
         10 . The method of  claim 9 , wherein the first step of determining determines potential x-y coordinate positions of the first finger touch and the second finger touch on the touch screen and wherein the second step of determining comprises the step of determining the minimum distance to one of the determined potential x-y coordinate positions of the first finger touch and the second finger touch and either, in one mode, the stored x-y coordinate position comprising the historical information or, in a second mode, a predicted x-y coordinate position of the first finger touch at the current time, in which the one of the determined x-y coordinate positions determined to be at the minimum distance comprises the current coordinate position of the first finger touch, wherein the predicted x-y coordinate position is based on the stored historical information. 
     
     
         11 . The method of  claim 10 , wherein the first or second mode is selected based on the proximity of the either the determined x-coordinates in the second step of determining to each other or the proximity of the either the determined y-coordinates in the second step of determining to each other. 
     
     
         12 . The method of  claim 11 , wherein the second mode is selected when the determined x-coordinates or y-coordinates, respectively, are proximate each other. 
     
     
         13 . The method of  claim 10 , wherein the historical information comprises at least a last known x-y coordinate position at the prior time to the current time and wherein the second step of determining in the second mode of operation comprises steps of:
 accessing the historical information which comprises the last known x-y coordinate position of the first finger touch;   determining the distance between the last known x-y coordinate position of the first finger touch and each of the potential x-y coordinate positions; and   selecting one of the determined potential x-y coordinate positions having the minimum distance to the last known x-y coordinate position as the current x-y coordinate position of the first finger touch at the current time.   
     
     
         14 . The method of  claim 10 , wherein the second step of determining in the second mode of operation comprises the steps of:
 predicting with the historical information a predicted location of the first finger touch at the current time;   determining the distance between the predicted location and each of the determined potential x-y coordinate positions; and   selecting the one of the determined potential x-y coordinate positions having a minimum distance to the predicted x-y coordinate position as the current x-y coordinate position of the first finger touch.   
     
     
         15 . The method of  claim 14 , wherein the historical information contains at least the last known x-y coordinate position for the first finger touch and a previous x-y coordinate position prior to the last known x-y coordinate position. 
     
     
         16 . The method of  claim 15 , wherein step of predicting to provide the predicted x-y coordinate position comprises the steps of:
 determining direction from the last known x-y coordinate position to a predicted new x-y coordinate position at the current time; and   determining distance based on the last known x-y coordinate position and the previous x-y coordinate position to define the distance of a predicted x-y coordinate position from the last known x-y coordinate position.   
     
     
         17 . An touch screen device for tracking finger movement over a surface, comprising:
 a touch screen having rows and columns;   a touch detector for detecting at which row and column of the touch screen a finger touch has occurred at a current time, and wherein multiple touches of at least first and second fingers at substantially the same time could result in finger touch ghosts such that an ambiguity exists as to which of the x- and y-coordinates at which a finger touch was detected is associated with at least the first finger such that multiple potential x-y coordinate positions exist for the first finger;   a memory for storing historical information of the x-y coordinate position of a finger touch of the first finger on the touch screen; and   a processor for analyzing the potential x-y coordinate positions as a function of the stored historical information and determining which is the correct x-y coordinate position as the current x-y coordinate position of the finger touch associated with the first finger at the current time, the processor storing the determined current x-y coordinate position in the memory as historical information for a future determination of the current x-y coordinate position.   
     
     
         18 . The device of  claim 17 , wherein the memory stores a last known x-y coordinate position of the finger touch of the first finger and the processor is operable to determine the distance to each of the potential x-y coordinate positions from the stored last know x-y coordinate position and select the one thereof with the minimum distance as the current x-y coordinate position of the finger touch associated with the first finger. 
     
     
         19 . The device of  claim 17 , wherein the memory stores a last known x-y coordinate position and an older x-y coordinate position relative thereto of the finger touch of the first finger and the processor includes a prediction engine that is operable to predict where the finger touch associated with the first finger will occur as a predicted x-y coordinate position based upon the last known x-y coordinate position and the older x-y coordinate position, and wherein the processor determines the distance to each of the potential x-y coordinate positions from the predicted x-y coordinate position and select the one thereof with the minimum distance as the current x-y coordinate position of the finger touch associated with the first finger.